Previously filed and commonly-assigned U.S. patent application Ser. No. 15/082,327 (“the '327 application”), entitled “Systems and Methods for Constructing and Testing Composition Photonic Structures,” which is incorporated by reference in its entirety herein, discloses a method of embedding stress indicator elements in the surfaces of structures to aid in determining ongoing stresses and/or deformations of the structure. The stress indicator elements can include an optical diffraction grating (e.g., photonic crystal, fiber Bragg grating) and, optionally, one or more fluorophore materials. The stress indicator elements are arranged so that deformation of the surface caused by, for example and without limitation, tensile stress, compressive stress, bending, temperature variations, and chemical composition changes or other material defects, changes the periodicity of the grating. When light is directed onto the structure including the stress indicator elements, light is diffracted by the elements into a pattern that corresponds to the periodicity of the grating. Changes in the periodicity caused by stresses and variations alter the diffraction pattern by shifting the wavelength of radiation at a particular angle of diffraction according to the well-known grating equation.
FIG. 1 shows an example embedded stress indicator element 10 disclosed in the '327 application. The element includes periodic components e.g., 12, 14, 16, each of which diffract wavelengths of light in varying angular modes (numbered m=0 through m=3). The periodic components of the stress indicator element, which can have a variety of shaped profiles, including sinusoidal, sawtooth, triangular, etc., include peak and valley features. The indicator elements are designed so that respective peaks and valleys of adjacent periodic features are a regular distance (d) apart. Deformations in the underlying structure will alter the inter-feature distance (d) of at least a portion of the components, which will, in turn affect the angle at which such altered components diffract incoming light.
While specialized detection and processing equipment can be used in this context for detecting radiation diffracted from the embedded elements in the structure and determining the deformation therefrom, such equipment can be cumbersome to transport to distant locations and difficult to set up in locations that have limited accessible space.
It would be useful to utilize the considerable processing capabilities of smart phones and tablets, which can be easily carried by field technical personnel to various sites and locations, in the performance of structural deformation detection. The present invention addresses these and other needs in the art.